1. Field of the Invention
This invention relates to a nano-technology, and in particular to carbon-coated metal oxide nano-particles and a method of preparing the same. The carbon-coated metal oxide nano-particles may be used as, for example, a photocatalyst.
2. Description of Related Art
Among all the functional materials to be synthesized on the nano-scale, metal oxides are particularly attractive candidates, from a scientific point and a technological point of view. The unique characteristics of metal oxides make them the most diverse class of materials, with properties covering almost all aspects of material science. The great variety of structures makes them the primary target in solid-state chemistry and provides the basis for designing new materials. In addition, metal oxide materials exhibit fascinating electronic and magnetic properties, including metallic or insulating and ferro-, ferri- or antiferromagnetic behavior. All these properties make metal oxides a vital constituent in technological applications like gas sensing, electroceramics, catalysis, energy conversion, data storage and so on. Among them, oxides of titanium, tin, iron and other metals that possess moderate band gaps can absorb visible to ultra-violet light to proceed photochemical reactions, such that these materials can serve as photocatalysts.
Some of these metal oxide photocatalysts are commonly used in daily life, and their potential in photochemical elimination/decomposition of organic pollutants for environmental purpose and in photovoltaics and solar energy utilization are widely recognized and are intensively studied worldwide.
A conventional method of preparing a metal oxide nano-structure is the aqueous sol-gel technique using a suitable precursor, but this technique has difficulties in reducing the particle size and controlling the reaction condition. Therefore, in recent years, the non-aqueous sol-gel technique is also adopted.
On the other hand, coating a layer of carbon on the surface of a nano-metal oxide photocatalyst can effectively improve the crystallinity stability, optical activity and the performance in adsorbing dye molecules or contaminants. In the conventional method of preparing carbon-coated metal oxide nano-particles, already formed metal oxide nano-particles and a polymer are mixed, and then high-temperature pyrolysis is conducted to carbonize the polymer on the nano-particles. However, the thickness of the carbon coating formed with the above method is usually not uniform, and the carbon content of the nano-particles is difficult to control.